This report describes the development and demonstration of an upgraded stench fire warning system for underground mines. Current systems release an ethyl mercaptan mixture into the compressed and/or ventilation air of a mine during an emergency. When smelling ethyl mercaptan, miners evacuate the mine according to predetermined plans. These systems, while simple, have problems with safety and reliability that can be overcome with the upgraded system. Thiophane, which is a different stench agent used in the upgraded system, is less toxic, less nauseating, and less corrosive then ethyl mercaptan. These features, and because thiophane does not react with iron oxides, make the upgraded system safer and more reliable. The system also uses a combination of two simple principles: a standpipe with pressure balancing to provide a constant head and a sized orifice to control the rate of release of the stench agent. The system enables mine operators to release the agent for a longer period, which provides better coverage and ensures that miners will not be exposed to potentially toxic concentrations of the stench agent.